TC1796
Peripheral Units (Vol. 2 of 2)
Analog-to-Digital Converter (ADC)
User’s Manual 25-41 V2.0, 2007-07
ADC, V2.0
25.1.8 Expansion of Analog Channels
The number of analog inputs can be expanded in a very flexible and powerful way to
satisfy the increased needs for analog inputs. In addition to the internal analog input
channel group selection, external analog multiplexers can be connected to each analog
channel if the following items are considered:
• Inverse current injection (overload) behavior
• ON resistance of the external multiplexer and load capacitance
• Timing of the external multiplexer
• Noise due to adjacent digital input pins
Note: The characteristics of the external multiplexers influence the accuracy of the A/D
Converters. An accuracy of
±
2 LSB @ 10-bit resolution is no longer guaranteed.
Two control lines are provided to drive external multiplexers, as shown in Figure 25-21.
Figure 25-21 External Expansion of Analog Channels
External analog multiplexers receive the select information CHCONn.EMUX[1:0] (and
optional GRPS, too) from the channel-specific control register individually for each
analog channel. Sequential sources derive the external multiplexer control information
from the conversion request control register (bit field CHIN.EMUX and QUEUE0.EMUX).
External
MUX
Internal
Analog
MUX
A/D
Converter
3
Control Registers
CHCONn
4
EMUX[1:0]
AIN0
AIN15
AN-0
AN-1
MCA06024
EMUX
AIN16
AIN31
Group 0Group 1
GRPS
AN-2
...
n
GRPS
1
AN-7
2
1
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